The present invention is directed to bicycles and, more particularly, to a sprocket assembly that forms a part of a bicycle transmission.
Bicycles typically include a frame, front and rear wheels, pedals that are used to rotate one or more front sprockets, a plurality of rear sprockets mounted to the rear wheel, and a chain that engages a front sprocket and one of the plurality of rear sprockets. If there is more than one front sprocket, then a front derailleur mounted to the frame in close proximity to the plurality of front sprockets is used to shift the chain among the plurality of front sprockets. A rear derailleur is mounted to the frame in close proximity to the plurality of rear sprockets to shift the chain among the plurality of rear sprockets. The rider typically uses manual, electric, or hydraulic control devices to control the front and/or rear derailleurs.
Small bicycles that have a frame capable of folding upon itself to facilitate carrying on public transportation or storage at work facilities are becoming more popular. Because such bicycles are carried and stored in crowded places, they should be very compact. Thus, the sizes of the frame and wheels are minimized accordingly. However, the smaller wheels must rotate faster than a conventional bicycle wheel in order to achieve the same bicycle speed. This, in turn, requires smaller rear sprockets if the bicycle is to achieve the same speed for a given pedaling rate. Unfortunately, the minimum size of any rear sprocket historically has been limited by the diameter of the wheel hub sprocket support on which the sprockets are mounted, which usually must be large enough to house internal components such as ratchet and pawl mechanisms. This makes it unfeasible to accommodate smaller diameter sprockets with conventional hub designs.